What is the structure of white light in terms of photons? If white light is just a mixture of all spectral colours, we name it "white". Does it mean it is a statistical mixture (rather than a quantum state) of photons of different wavelengths?
 A: The colour is not a property of the photon or the light; it is how our eyes perceive photons of different energies. 
When many photons of different colours fall on your eye proportionally, your eye perceives it as white colour. However, in reality, there is no real magic happening.
Our eyes consist of two types of cells, namely rods and cones. The rods are sensitive to the intensity of light and the cones are sensitive to colour. Our eyes contain broadly three types of cone cells, one for each of the primary colours (red, green and blue).
When a mixture of red, green and blue light falls on the cone cells, our brain interprets it as white light. When a mixture of red and green light falls on our cone cells, our brain interprets it as yellow light. The light which falls on the cone cells stimulates the cone cells of different kinds to varying degrees and this is how we see colour. The colour isn't really a property of photons or light; it is merely how our eye perceives a collection of photons or light rays. For our eye, in terms of the white colour, the white light is statistical mixture of photons of different wavelengths.

Picture Credits: Why do we see in colour? livescience.com
